Quick Facts: Hazards of the CANDU-6

Background

Atomic Energy of Canada Limited (AECL) developed the Candu-6
reactor in the early 1970s. The CANDU-6 is the only reactor AECL
has sold.

Nine CANDU-6s have been built internationally in China (2),
Argentina (1), South Korea (4) and Romania (2). Two were built in
Canada - Point Lepreau in New Brunswick and Gentilly-2 in
Quebec.

Despite its current promotion of the prototype Advanced CANDU
Reactor (ACR), the CANDU-6 remains central to AECL's business
plans. AECL hopes to sell additional CANDUs to Argentina, Romania
and Turkey etc.

Ontario abandoned its plan to build a CANDU-6 reactor in 2006
because the design did not meet modern safety requirements.

The CANDU-6 poses unique nuclear safety and proliferation risks
that should call into question Canada's continued support of AECL's
marketing of this antiquated design and the refurbishment of
operating CANDU's in Canada.

A CANDU Design Flaw: Positive Reactivity

The world's first significant international nuclear accident
occurred in 1952 when Atomic Energy of Canada Limited's (AECL) NRX
reactor experienced a power pulse, causing a hydrogen explosion and
melting of fuel assemblies.

A central cause of the NRX accident was the reactor's "positive
reactivity," which refers to the tendency of the reactor's power to
increase, potentially in an explosive pulse (p. 19).

Following the NRX accident most international regulators and
vendors decided to shun reactors with positive reactivity due to
the inherent hazard of design. The Canadian nuclear industry and
its regulator, however, decided to tolerate this design flaw in
order to accommodate the CANDU design (pp. 19 - 20).

AECL's continued existence depends on Canada's nuclear
regulator continuing to accept positive reactivity, which is
contrary to the direction taken by other international regulators
(p. 29).

In 1972, AECL started up a prototype reactor called Gentilly-1
near Trois-Rivières Quebec. The magnitude of positive reactivity
exhibited by Gentilly-1 was so great it could not operate
stably.

There was concern that the reactor's containment would not
withstand an explosive power pulse arising from failure of the
emergency shut down system. Gentilly-1 was permanently shut down in
1977 (pg. 20).

Despite evidence following the Gentilly-1 fiasco that a
mainstream CANDU could experience an explosive power pulse,
Canada's nuclear regulator did not prohibit positive reactivity.
Instead the regulator required all new CANDU reactors to have two
independent emergency shutdown systems, which diverged from the
approach taken by most other international regulators (p. 21).

The ability of CANDU shutdown systems to operate under accident
conditions has not been confirmed by test or experience (p. 21).
Confidence in the estimated effectiveness of CANDU shutdown systems
in accident situations is low because of the significant
uncertainties in modeling such situations (p. 23).

The CANDU and Chernobyl RBMK reactor designs both exhibit
positive reactivity. A significant contributor to the 1986
Chernobyl accident was positive reactivity (p.38).

The Chernobyl accident spurred Canada's nuclear regulator to
reassess its assumptions regarding the hazards posed by positive
reactivity in CANDU reactors. Work proceeded very slowly. Studies
eventually showed a high degree of uncertainty in the assumptions
underlying safety assessments for CANDU reactors (p. 20).

Anticipating applications for new reactors, the CNSC proposed a
new regulatory framework for licensing reactors based on
international safety standards in 2005, which "prioritized"
reactors with negative reactivity (p. 29).

AECL complained that the application of international standards
would have negative impacts on the marketing prospects of the
CANDU-6 internationally and would reflect badly on operating CANDUs
in Canada (p. 29).

If modern international safety standards were strictly applied,
a reactor with positive reactivity such as the CANDU-6 could not be
built (p. 29).

In 2008, AECL was forced to abandon the commissioning of two
small MAPLE reactors at Chalk River because they exhibited
uncontrollable positive reactivity (p. 7).

In 2001, AECL began a marketing push in Canada, the United
States and the United Kingdom for its prototype Advanced Canada
Reactor (ACR). Unlike the CANDU-6, the ACR is intended to have
negative reactivity in order to meet modern licensing requirements
(p. 7). To do this, it uses slightly enriched uranium instead of
natural uranium, and light-water cooling.

A CANDU-6 Vulnerability: Terrorism

The CANDU-6 is a pre-September 11th design and was not designed
to resist a terrorist attack.

In 2006, Ontario abandoned its plan to build a new CANDU-6
because of the design changesrequired to meet post-September 11th
safety requirements (p. 9).

While requirements for reactors to be more robust against
terrorist attacks continue to evolve sinceSeptember 11th, it is
clear that the CANDU-6 would not meet current standards if they
wererigorously applied (p. 36).

Proliferation Arms Proliferation and the CANDU-6

The CANDU-6's use of natural uranium makes it attractive to
countries hoping to acquire fissile material (plutonium or
high-enriched uranium) for use in nuclear weapons without the need
for enrichment facilities.

The CANDU-6 practice of online re-fueling makes it difficult to
detect and prevent the diversion of used nuclear fuel for the
possible use in atomic weapons (p. 24)

India produced plutonium for its 1974 nuclear weapons test in
its Canadian supplied CIRUS reactor, which used natural uranium
fuel (p. 23).

It is suspected that Pakistan has used its Canadian supplied
KANUPP reactor to produce military plutonium (p. 23-24).

Three to four kilograms of plutonium is sufficient to produce
an atomic bomb. (p. 13)

Canadian reactors will have produced 170 thousand kilograms of
plutonium through 2010. (p. 13)

AECL is interested in selling additional CANDU-6 reactors to
countries such as Turkey, India and Jordan that may be interested
in acquiring a ready option for diverting spent reactor fuel for
production of nuclear weapons.

CANDU Life-Extension and a Weak Regulator

The economic case for re-building and extending the life of
CANDU reactors, such as Quebec's Gentilly-2 nuclear station, is
weak and dependent on the rigour with which the CNSC imposes modern
regulatory requirements and upgrades to the reactors (p. 33).

The Canadian Nuclear Safety Commission has significantly
weakened its modernized safety requirements to accommodate the
design flaws of operating designs in Canada since they were first
drafted in 2005 (p. 28-29).

The CNSC's imposition of international safety standards to the
pre-licensing of the CANDU-6 in 2006 created a tension between the
CNSC and the federal government because of the negative impact it
had on AECL's ability to retain market share in Ontario (p.
9).

CNSC president Linda Keen was subsequently fired by the Harper
government for her handling of the socalled radio-isotope
crisis.

Hydro-Quebec has decided to proceed with the life-extension of
the Gentilly-2 nuclear station before it has completed the safety
reviews required by the CNSC. This leaves the estimated cost for
rebuilding the Gentilly-2 nuclear station open to considerable
"regulatory risk" if the CNSC applies modern regulatory
requirements stringently (p. 32).

The CNSC's approach to life-extension has been improvised and
dependent on secretive and ad hoc negotiations between it and
reactor operators on the rigour with which modern regulatory
requirements will be imposed. (p. 32- 34). In such an environment,
the CNSC may be overly apt to prioritize the business interest of
nuclear operators over the stringent application of safety
standards.